Rotation sensors mounted to bearings are used to control rotational speeds, rotational directions, rotation angles, etc., of e.g. motor shafts and vehicle axles. The rolling bearing of such a bearing assembly includes a stationary bearing race fitted to a stationary member such as a motor housing or a suspension of a vehicle, and a rotary bearing race fitted to a rotary member which is rotated about its own axis.
To use this type of bearing assembly, the rolling bearing is mounted between a rotary shaft, such as a motor shaft or a vehicle axle, and a stationary member such as a housing; a magnetic sensor unit is supported on the peripheral surface of the first bearing race fitted to the stationary member that is formed with the raceway; an encoder is mounted to the second bearing race fitted to the rotary shaft so as to rotate in unison with the rotary shaft, forming a predetermined gap between the encoder and the magnetic sensor held by the magnetic sensor unit; and the magnetic sensor is connected to an external device through wires. The encoder converts the rotation of the second bearing race and thus the rotation of the rotary shaft to a change in magnetic which is detected by the magnetic sensor. The detection signal from the magnetic sensor is transmitted to the external device through the wires. The external device uses the detection signal to control the rotational speed, rotational direction, rotation angle, etc., of the rotary shaft.
The sensor holder is supported on the first (stationary) bearing race because the wires and sensor can be easily positioned relative to the first bearing race. The sensor holder is an annular member so that the sensor holder can be fitted to the first bearing race. In particular, the sensor holder, which carries the magnetic sensor, is press-fitted to the first bearing race so as to be fixed to the first bearing race. The encoder, which is rotationally fixed to the second bearing race converts its rotation to a change in magnetic field. The encoder can be easily fixed to the peripheral surface of the second bearing race or another rotary member through a core bar or directly by press-fitting or by means of nuts.
As described above, with the rolling bearing mounted between the stationary member and the rotary member, with the sensor holder mounted to the first bearing race, and with the signal from the magnetic sensor sent to the external device through wires extending outwardly from the sensor holder, detection can be made by the encoder and the magnetic sensor (see e.g. JP Patent Publication 2002-40037A).
One known conventional sensor unit is a sensor holder which is a combination of an annular sensor support body and a sensor case to which the magnetic sensor is fixed. The sensor case insulates and protects the magnetic sensor circuit from outside. The sensor case includes a sensor mounting portion made of a resin and defining an open recess in which the sensor circuit is fixedly mounted. At least the sensor circuit is covered by a protective material such as resin molding or a lid. When the sensor case is inserted into the sensor support body, the sensor support body is configured to guide the sensor case to a fitted position where the magnetic sensor is located in a detecting position.
A conventional such sensor support body is typically in the form of a metal sheet fixed to the peripheral surface of the first bearing race formed with the raceway by press-fitting. Such a sensor support body has an annular sensor case inserting hole open at one axial end of the sensor support body and closed at the other axial end by an end wall. The sensor case has an insert portion adapted to be inserted into the sensor case inserting hole in the axial direction. Before inserting the insert portion into the inserting hole, adhesive is applied to the surface of the insert portion and/or the surface of the inserting hole. When the insert portion is inserted into the inserting hole until the insert portion abuts the end wall, the sensor case is fitted in the sensor support body in the fitted position where the magnetic sensor is located in the detecting position. The sensor support body has a plurality of circumferentially spaced apart bent claws which axially keep the sensor case in the fitted position (see e.g. JP Patent Publication 2002-295465A).
If the first bearing race (i.e. stationary bearing race) is fitted to the stationary member, the stationary bearing race may creep due to the imbalance of the shaft. If creeping is a concern, the stationary bearing race may be fitted to the stationary member by press-fitting.
But if, due to some problems in assembling, the stationary bearing race cannot be press-fitted to the stationary member, the wires, which extend from the sensor holder, could be broken due to creeping of the stationary bearing race. In the arrangement of JP Patent Publication 2002-295465A, when the stationary bearing race creeps, the sensor support body, which is fixed to the stationary bearing race, rotates together with the stationary bearing race. Excessive creep, i.e. rotation, of the stationary bearing race could pull and break the wires connecting the magnetic sensor circuit fixed to the sensor case to the external device, which is a member of a system to which the bearing assembly is mounted.
In JP Patent Publication 2002-295465A, no consideration is given to the possibility of reusing the sensor case after the roller bearing becomes useless due e.g. to creeping of the stationary bearing race or due to natural aging of the bearing. In order to reuse the sensor case of JP Patent Publication 2002-295465A, for example, the sensor case has to be removed from the sensor support body by breaking the adhesive bond therebetween and bending all of the bent claws of the sensor support body. It is thus extremely troublesome to remove the sensor case from the sensor support body. Also, since the guide surface of the sensor case is damaged by the adhesive, it is difficult to combine this sensor case with a new sensor support body.